Concerning an internal combustion engine equipped with a supercharger in an air intake pathway, there has been known such a configuration as to be equipped with a bypass pathway for allowing downstream and upstream sides of a supercharger to come in communication with each other and also equipped with a bypass valve which can open or close the bypass pathway. Patent Document 1 discloses an arrangement where the bypass pathway is provided in parallel with a mechanical supercharger perpetually driven by the engine output so that the bypass valve disposed within the bypass pathway is opened during a low load state to relieve the supercharging pressure. Patent Document 2 discloses an arrangement where the bypass pathway is provided in parallel with a mechanical supercharger driven according to engine-operating conditions and the supercharging pressure is controlled by the opening degree of the bypass valve.
In the above-mentioned arrangement including a bypass pathway which allows the downstream and upstream sides of the supercharger to come in communication with each other, when the bypass valve opens and an intake air is put into circulation from the downstream side of the supercharger to the upstream side of the supercharger, a portion of the intake air may sometimes flow back to the more upstream side of the air intake pathway so as to reach to an air flow meter. Hence there has been a problem that if the air flow meter has good responsivity the backflow components may be detected by the air flow meter to cause some errors.